For some time now, airport concourses have been secured areas to which only authorized individuals (employees or screened passengers) are permitted access. Nonetheless, these are areas of high traffic volume with large groups of people going in one direction to reach a gate, and in the opposite direction to retrieve their luggage, access parking or ground transportation, etc. While perhaps the readiest example of a high volume, secure area, there are other areas such as those in government offices, military facilities, etc. where relatively large numbers of people are constantly moving into and out of secure areas.
It is commonplace with these secure areas that while access into the area requires movement through some type of screening, the exit passageways are relatively open. That is, there are usually no fixed barriers such as doors or gates through which a person has to pass so that people can move rapidly and unencumbered through the exit. However, there is usually at least one guard posted in this egress passage to prevent people from entering into the secure area through it, thereby bypassing the security screening. While guards are usually effective, there are, nevertheless, numerous instances of security breaches in which someone has gotten past the guard and escaped into the secure area. When this occurs in an airport, the concourse is typically evacuated, and all passengers waiting for planes have to be re-screened. As a result, numerous flights are delayed, all at an enormous cost in time and money to the airport, the airlines, and the passengers.
Studies have shown that security guards or monitors, regardless of how dedicated, do not provide the vigilance that is required for prolonged periods of time. After a while, they become tired and can be distracted. Or, it is not uncommon for a guard to be diverted from his or her task in order to render assistance to someone in need. In either instance, the way is made clear for a wrong-way traveler to enter into the secure area through the exit passage, and to do so undetected.
It is known for airport security systems to include video monitors installed in an exit passage to view movement of people through the passage. It is also known to sense wrong-way movement of people in this area, and to “sound” an alarm when wrong-way movement is detected. Typically, when an alarm occurs, frames of imagery showing the passage and the people in it at the time of the alarm are captured and analyzed. A drawback with conventional analysis is that it looks for movement only in one direction through the passage. This is so, even though these systems may be capable of perceiving movement in both directions.